The present invention relates to a method of manufacturing an Arsenic-including compound semiconductor device so that uniform electrical activation is obtained over the whole of the slice.
Generally, in a semiconductor device of an As compound wafer, such as GaAs wafer, it is necessary to implant silicon ions (or the like) into the wafer to form an active layer. When forming an active layer, in order to promote the substitution of arsenic ions in the wafer for the implanted silicon ions, high temperature treating (so-called annealing) is needed. At this time, since the evaporation temperature of arsenic is lower than that of gallium, the arsenic ions in the wafer surface are evaporated by the annealing heat, which leads to a reduction of the electrical activation.
Usually, therefore, after ion implantation, the wafer is annealed in an atmosphere containing arsenic at a pressure of 1 or 2 Torr. This pressure is called the As overpressure. Evaporation of arsenic may be prevented by setting this As overpressure higher than the pressure to prevent As evaporation (the pressure at which As begins to be decomposed from the wafer).
A method is also known for forming a cap composed of silicon oxide film and plasma nitride film on the surface of a wafer, and preventing As evaporation during annealing by this method.
In the method of applying the As overpressure, however, it is difficult to supply the gas containing As uniformly on the whole area of the slice surface. Yet, the arsenic does not evaporate uniformly over the slice surface. Rather, the arsenic intensifies the dislocation. Owing to such difficulty in control of gas flow rate and nonuniformity of As evaporation distribution, it is extremely difficult to prevent evaporation of arsenic uniformly over the whole area of the slice.
On the other hand, in the encapsulation method of the wafer surface with silicon oxide film or plasma nitride film for the passivation of GaAs wafer, the evaporation of As becomes nonuniform due to properties of these films (quantity of hydrogen in the film, presence of pinholes, etc.), so that the electrical activity becomes nonuniform.
It is hence a primary object of the invention to present a method of manufacturing an Arsenic-including compound semiconductor device capable of solving such conventional problems.